The present invention concerns a portable device for measuring a position, a shape and/or a size of an object. The device has a carrier element, a transmission unit for generating and transmitting visible radiation towards the object and a receiving unit for receiving the radiation imaging the object. The transmission unit and the receiving unit are mounted to the carrier element in a defined position relative to each other.
Portable in the sense of the present invention means that the device is relatively small and can be guided either manually e.g. via a measuring arm, a coordinate measuring machine or by an industrial robot, and introduced to the object to be measured. Measuring arms are distributed e.g. by the company Faro Technologies, Inc., Lake Mary, Fla., USA. Coordinate measuring machines are distributed e.g. by the company Carl Zeiss Industrielle Messtechnik GmbH, 73446 Oberkochen, Del. or by the company Wenzel Präzision GmbH, 97859 Wiesthal, Del. The device may be moved on the coordinate measuring machine either directly by hand or automatically via a motorized position head (e.g. by the company Renishaw, New Mills, Wotton-under-Edge, GB).
The location of an object is defined by its position (x, y, z coordinates) and also its orientation (angle with respect to the x, y, z axis). When the absolute or relative position of the device is known, the position of the object can be determined using the device. The device can also determine the shape and size of the object. The shape and size of the object can be determined with and without knowledge of the exact position of the device. Depending on the design of the device, the position of the object or the size and the shape of the object can be measured in one-dimensional, two-dimensional or three-dimensional space.
When the spatial position of the object to be measured is known, the device of the above-mentioned type can be used to adjust the position of a tool or gripper mounted to the robot arm. Towards this end, the device measures the position of the object, and the position of the tool or gripper is varied until the measured position of the object corresponds with the actual position. A correction matrix can be determined for control of the robot arm in dependence on the actual sizes of that arm.
The transmission unit is designed as a light source, e.g. as a laser and, in particular, as a semi-conductor laser (diode laser). It may also comprise e.g. a white light projector with different fixed and variable patterns. The transmission unit can transmit light in a range which is visible or invisible to the human eye. The receiving unit is designed as an electronic camera with a semi-conductor element of matrix-like construction for video recording, in particular with a CCD (Charged Coupled Device)—or a CMOS (Complementary Metal-Oxide Silicon) chip. A control unit for the transmission unit and an evaluation unit for the receiving unit can either be integrated in the device or be disposed outside of the device.
The transmission unit and the receiving unit are each mounted to the carrier element in a defined position. The position, the shape or the size of the object are measured e.g. using the so-called triangulation method. The laser triangulation method is explained in detail in WO01/69172 (see FIG. 2 thereof), the entire disclosure of which is hereby incorporated by reference. The position, shape and size of the object can be measured e.g. by stereo image processing, by photogrammetric methods or by methods with structured light.
A device of the above-mentioned type is distributed e.g. by the company Perceptron, Inc. 47827 Halyard Drive, Plymouth, Mich. 48170 USA. Such a device and the use of such a device are known e.g. from U.S. Pat. No. 4,645,348 and U.S. Pat. No. 6,166,811. The conventional device comprises a carrier element in the form of a housing which is completely closed except for openings for transmission and receiving unit radiation. The housing has at least one transmission unit formed as a light source which emits radiation visible to the human eye onto the object to be measured. The transmission unit could, however, also transmit invisible UV (ultraviolet) or IR (infrared) radiation. The known device also comprises a receiving unit which receives radiation reflected from the object and converts it into electric signals which are proportional to the intensity of the reflected radiation. The receiving unit comprises e.g. a CCD chip or a CMOS sensor. The receiving unit may comprise conventional camera optics, spectral filters, polarization filters or other filters. The transmission unit and the receiving unit are mounted at predetermined positions in the housing. The housing is then closed and access to the transmission unit and/or the receiving unit from outside the housing is no longer possible.
The device including carrier element, at least one transmission unit and at least one receiving unit is also called a sensor. The transmission unit and the receiving unit each have an optical axis, wherein the optical axes of the two units intersect in a point of intersection at which the object to be measured is disposed. The measuring distance between the device and the object is determined by the inclination of the optical axes relative to each other and by the separation between the transmission and receiving units. The separation between transmission unit and receiving unit determines the length of the device. The known device may have numerous embodiments. The embodiments are designed e.g. for different measuring distances or comprise different transmission units (different frequency, shape, pattern of the emitted light) and/or different receiving units (different optics with different foci, different filters).
This requires production of a plurality of different embodiments of the device for the various applications which makes production of the conventional devices relatively demanding and expensive. The end user must buy and store a plurality of different embodiments of the device for different applications. This results in considerable costs for purchase, storage and maintenance of the conventional devices.
The manufacturers of the conventional devices are obliged (for economic reasons) to keep the range of housing lengths and measuring distances as narrow as possible. For this reason, sensors are available with measuring distances of 400 mm, 500 mm, 600 mm and some other measuring distances determined by the manufacturers. Intermediate sizes are not offered. The conventional devices are therefore not adjusted to the measuring task but vice versa: the measuring conditions must be adjusted to the given technical features of the device, in particular, the measuring distance. Even when the measuring distance must be changed for a subsequent application, the sensor cannot be simply adjusted, rather must be entirely replaced. This results in substantial costs for the end user.
It is the underlying purpose of the present invention to design and further develop a device of the above-mentioned type for measuring an object, wherein the device is highly variable and is flexible with regard to applications having differing requirements. The device should also be as small and compact as possible.